The present invention relates to the preparation of a labelled compound and to the manipulation of a gaseous radiosotope in a double-sealed state.
Glass apparatus are used in general for sealing hermetically gaseous radioisotopes. However, with the conventional hoods the human body and environments would undoubtedly be contaminated by the leaking gaseous radioisotopes on breakdown of the glass apparatus. Accordingly, it is required that gaseous radioisotopes can be manipulated with use of an apparatus system sealed under vacuum and also such an apparatus system can be handled in a hood sealed hermetrically.
Labelled compounds are extensively being utilized as a tracer in the various fields such as physics and chemistry, medical science, biology, pharmacology, biochemistry, and industries. For preparing the labelled compounds there is a method utilizing an exchange reaction of hydrogen of a sample with tritium which takes place by .beta.-ray of tritium. This method, being called a gas exposure method, includes enclosing a compound to be labelled and tritium gas within a container, allowing them to stand for a desired time and thereafter recovering tritium gas and producing a labelled compound. In addition to this method there are improvements of the gas exposure method, such as an electrical discharge method, catalytic method, irradiation method of ultraviolet ray, and radiation method, and a catalytic reduction method. It is well known that apparatus provided with Toepler's pump have hitherto been used for realizing these methods. However, such the prior art have the following disadvantages:
1. The attached instruments such as vacuum pump and exhaust pipes are contaminated by tritium.
2. By leakage of tritium absorbed on the innerside of apparatus and the instruments attached thereto a tritium concentration in the chamber increases and the workers are exposed to radiation.
3. Pollution of the atmosphere is caused by release of the air containing a high concentration of tritium from the exhaust port of laboratories.
4. A large-sized waste contaminated with tritium, such as disused apparatus, vacuum pump and other attached devices is generated.
5. When a broken out glass apparatus is repaired by meltsealing of glass, tritium adsorbed on the glass is generated in large quantities. There is a danger that tritium is generated in large quantities in the oil exchange of the vacuum pump.
6. It takes a long time for assembling the necessary apparatus. Particularly when a vacuum grease for fitting glass cocks is renewed, the gloves are contaminated because they come into contact with the grease contaminated by tritium. Also the contamination is extensively spread by touching other things with the contaminated gloves.
7. When apparatus, instruments attached thereto, hoods, and structures such as the floor and ceiling are contaminated by tritium, removal of the contamination requires a great deal of labor and expense.
8. The conventional method requires a large-sized hood because the apparatus to be used becomes large-sized.
9. Although it is necessary to elevate the reaction pressure for increasing a specific activity of the labelled compound and reaction efficiency, there is a limit as a matter of course in case of the apparatus with use of the Toepler's pump.
10. There is need to seal the cocks during the reaction because there is danger of tritium gas leaking therefrom. However when the gas pressure of the reactor is close to atmospheric pressure, it is difficult to seal the cocks.
11. When filtration is effected for removing the catalyst after completion of the catalytic reduction, tritium adsorbed on the catalyst is scattered in large quantities and therefore gives rise to radioactive exposure to the workers and pollution of the air in the chamber and outdoors.
On the other hand, tritium gas to be used as the preparation material of labelled compounds is economically advantageous to be purchased in an ampoule with large quantities. In many cases, for practical purposes tritium gas is manipulated in the form of several or several tens ampoules with small quantities separately. Therefore it is necessary to itemize the large quantities of tritium gas to the ampoules with small quantities. The apparatus with the Toepler's pump have hitherto been utilized for the itemizing operation. The method using such conventional apparatus has the disadvantages as in (1) to (8) mentioned hereinbefore.
Furthermore, it is necessary to increase safety that the apparatus of manipulating such gaseous radioisotope as tritium gas are used in a closed chamber. For this purpose systems having a glove-box, draft or hood provided with ventilation equipment have been hitherto used. According to these systems, the ventilation equipment is always operated under a semi-closed state or the particular treatment apparatus are provided in one-or multiple-plates between the ventilation equipment.
A treatment apparatus having high efficiency must be provided with to satisfy these systems. In some of the gaseous radioisotopes such apparatus are difficult to set up or become large-sized and expensive. In case of the treatment apparatus having low efficiency, when an accident happens, there is danger of the radioisotope gas with high concentration being diffused or scattered, as it is untreated, in and out of the laboratories. This is quite unsafe and therefore prohibited by laws. The exhaust gas below tolerance limits must be discharged.
On the other side, the gaseous radioisotope manipulating apparatus are usually operated in the glove box, hoods or drafts while ventilating the chamber directly or through treatment apparatus. At that time, for example, powdered substances often are scattered by the air pressure due to flowing of the gases. Such substances thereof must be manipulated without operating the ventilation equipment. Similarly, weighing by even balance is effected without operating the ventilation equipment. However this is sometimes accompanied by a very dangerous aspect because the radioisotopes are gradually accumulated.
In the conventional systems, thus, there are possibilities of the radioisotopes with high concentration being discharged through the ventilation equipment to the outdoors and the safety is maintained through dilution by diffusion of the exhaust gas into the atmosphere. In this connection the important problems are that the contamination of ducts leading from the ventilation equipment to the outdoors are accumulated and also the atmosphere is polluted. When ducts and the attached parts become obsolete, contamination in and out of the laboratories by them can not be disregarded. As particularly such a radioactive gas as tritium has a property of adhering or permeating to various things, it also becomes an issue. Accordingly, it is necessary to decrease the concentration of the radioisotope in the ducts during manipulation.
A main object of the present invention is to provide a system wherein gaseous radioisotopes can be safely manipulated with use of apparatus hermetically sealed under vacuum and particularly a double-closed system wherein such sealed apparatus can be also handled in a sealed chamber for increased safety.
Another object of the present invention is to provide a process for preparing safely and simply labelled compounds and apparatus to be used in carring out the same, which are applicable to the gas exposure method and its improvements such as electric discharge method, catalytic method, irradiation method of ultraviolet ray and radiation method or the catalytic reduction method, thereby overcoming all of the disadvantages of the prior art.
Further another object of the present invention is to provide a method for itemizing safely and simply a definite amount of gaseous radioisotopes.
Still another object of the present invention is to provide a closed system for handling a gaseous radioisotope manipulating apparatus in a closed state and discharging gases below tolerance limits to the outdoors.